Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Brine

Ammonia

Freon

2. A bootstrap air cooling system has

Three heat exchangers

One heat exchanger

Two heat exchangers

Four heat exchangers

3. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Evaporator tubes

Refrigerant cooling tubes

Condenser tubes

4. The curved lines on a psychrometric chart indicates

Relative humidity

Dew point temperature

Wet bulb temperature

Dry bulb temperature

5. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

6. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Positive

Zero

Negative

7. The capillary tube, as an expansion device, is used in

All of these

Domestic refrigerators

Room air conditioners

Water coolers

8. Freon group of refrigerants are

Nontoxic and non-inflammable

Inflammable

Toxic

Non-inflammable and toxic

9. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

10. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

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11. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Evaporator and compressor

Compressor and condenser

Condenser and receiver

12. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

13. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Absorber

Condenser, absorber and separator (rectifier)

Condenser

14. Critical temperature is the temperature above which

Water will evaporate

Water will never evaporate

A gas will immediately liquefy

A gas will never liquefy

15. A thermostatic expansion valve in a refrigeration system

None of the above

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

16. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

2.33

1.33

4.33

17. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Less

Equally

18. The domestic refrigerator uses following type of compressor

Centrifugal

Axial

Piston type reciprocating

Miniature sealed unit

19. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Wet bulb temperature of air

Dew point temperature of air

Dry bulb temperature of air

20. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

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21. The freezing point of sulphur dioxide is

-77.7°C

-135.8°C

-56.6°C

-75.2°C

22. Most thermostatic expansion valves are set for a superheat of

15°C

10°C

20°C

5°C

23. The boiling point of ammonia is

-10.5°C

-33.3°C

-77.7°C

-30°C

24. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Takes place at constant pressure

Involves no change in volume

Takes place at constant temperature

25. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.4

0.67

0.376

26. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

27. For obtaining high COP, the pressure range of compressor should be

Low

Optimum

High

Any value

28. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

1.25

5.12

29. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

At critical Temperature

Near critical temperature of refrigerant

Much below critical temperature

30. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

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31. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 3

1: 1

1: 9

9: 1

32. Which of the following cycles uses air as the refrigerant?

Ericson

Carnot

Bell Coleman

Stirling

33. Rating of a domestic refrigerator is of the order of

40 tons

0.1 ton

10 tons

5 tons

34. The vapour compression refrigerator employs the following cycle

Carnot

Rankine

Reversed Rankine

Reversed Carnot

35. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Wet vapour

Saturated liquid

Superheated vapour

36. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Any one of the above

Always more than unity

Always less than unity

37. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

38. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

15 bar

2 bar

30 bar

39. Which of the following is not a desirable property of a refrigerant?

Low boiling point

Large latent heat

Good electrical conductor

High risibility with oil

40. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

Super-cooling

None of these

Normal cooling

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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